REVIEWOpenAccessUnderstandingtumorecosystemsbysingle-cellsequencing:promisesandlimitationsXianwenRen*,BoxiKangandZeminZhang*AbstractCellularheterogeneitywithinandacrosstumorshasbeenamajorobstacleinunderstandingandtreatingcancer,andthecomplexheterogeneityismaskedifbulktumortissuesareusedforanalysis.Theadventofrapidlydevelopingsingle-cellsequencingtechnologies,whichincludemethodsrelatedtosingle-cellgenome,epigenome,transcriptome,andmulti-omicssequencing,havebeenappliedtocancerresearchandledtoexcitingnewfindingsinthefieldsofcancerevolution,metastasis,resistancetotherapy,andtumormicroenvironment.Inthisreview,wediscussrecentadvancesandlimitationsofthesenewtechnologiesandtheirpotentialapplicationsincancerstudies.IntroductionAsinglecellistheultimateunitoflifeactivity,inwhichgeneticmechanismsandthecellularenvironmentinter-playwitheachotherandshapetheformationandfunc-tionofsuchcomplexstructuresastissuesandorgans.Dissectingthecompositionandcharacterizingtheinter-action,dynamics,andfunctionatthesingle-cellresolutionarecrucialforfullyunderstandingthebiologyofalmostalllifephenomena,underbothnormalanddiseasedcon-ditions.Cancer,adiseasecausedbysomaticmutationsconferringuncontrolledproliferationandinvasiveness,couldinparticularbenefitfromadvancesinsingle-cellanalysis.Duringoncogenesis,differentpopulationsofcan-cercellsthataregeneticallyheterogeneousemerge,evolve,andinteractwithcellsinthetumormicroenvironment,whichleadstohostmetabolismhijacking,immuneeva-sion,metastasistootherbodyparts,andeventualmortality.Cancercellscanalsomanifestresistancetovari-oustherapeuticdrugsthroughcellularheterogeneityandplasticity.Cancerisincreasinglyviewedasa‘tumoreco-system’,acommunityinwhichtumorcellscooperatewithothertumorcellsandhostcellsintheirmicroenviron-ment,andcanalsoadaptandevolvetochangingcondi-tions[1–5].Detailedunderstandingoftumorecosystemsatsingle-cellresolutionhasbeenlimitedfortechnologicalreasons.Conventionalgenomic,transcriptomic,andepi-genomicsequencingprotocolsrequiremicrogram-l...
